Overpressured thin-layer chromatography

The properties, apparatus and applications of overpressured thin-layer chromatography (OPTLC) have been reviewed. In the Introduction planar chromatography has been briefly characterized, with particular attention to TLC. The general properties of OPTLC and methods of development of chromatograms in this technique have been then given. The construction of chambers and equipment for OPTLC has been described, paying attention to two-dimensional columns. The properties of chambers for OPTLC have been characterized considering the flow of eluent, sorbent-eluent interactions and the efficiency of various systems. OPTLC, TLC and HPTLC have been compared and also a comparison between OPTLC with a constant (linear) eluent flow-rate and with a decreasing eluent flow-rate has been made. Analytical applications of OPTLC have been described and examples of separations of mixtures have been given.     

Photoinduced electron transfer via nonbuttressed metal-metal bonds. The photochemical study of binuclear complexes with platinum-thallium bonds

The photochemistry of binuclear metal-metal bonded complexes [(NC) 5Pt-Tl(solv) x ] (solv is water or dimethylsulfoxide) has been studied in aqueous and dimethylsulfoxide solutions. Both stationary and nanosecond laser flash photolysis have been carried out on the species. The metal-metal bonded complexes have been photolyzed by irradiation into the corresponding intense MMCT absorption bands. Photoexcitation results in the cleavage of the platinum-thallium bond and the formation of a solvated thallous ion and a cyano complex of platinum(IV), [Pt(CN) 5(solv)] (-), in both cases. The species have been characterized by multinuclear NMR and optical spectroscopy. The products of the photoreaction indicate a complementary two-electron transfer occurring between platinum and thallium ions in the binuclear Pt-Tl species. Quantum yield values for the photodecomposition of the species have been determined. The intermediates of the photoinduced metal-to-metal electron transfer have been detected and characterized by optical spectroscopy. The kinetics of transient formation and decomposition have been studied, and mechanisms of the photoactivated redox reaction have been suggested.     

Vibrational spectra,normal coordinates and infrared intensities of four isotopic phenyl acetates

The i.r. and Raman spectra of phenyl acetate and its deuteromethyl and deuterophenyl derivatives have been recorded. The fundamental frequencies of the four isotopic species have been assigned by referring to the Raman depolarization ratios and isotopic frequency shifts. The normal coordinates have been calculated on the basis of a valence force field. The general valence type force constants have been refined by the least-squares method. The i.r. spectra of the four isotopes have been simulated by using the obtained force field in combination with a suitable set of the atomic charges and their fluxes.     

Frequency-modulated simultaneous multielement atomic absorption spectrometry using electrothermal atomizer and deuterium background correction

Characteristic data of the frequency-modulated simultaneous multielement atomic absorption spectrometry (FREMSAAS) using electrothermal atomizer with deuterium background correction, have been determined. The data obtained have been processed by using several statistical tests recommended for quality control purposes. The instrumentation has been presented as well as procedures of separating elements into measure groups and fixing of variable conditions. Detection limits, characteristic masses and working ranges have been given for the eleven elements examined. The data have been in good agreement to results obtained with conventional one-channel AAS instruments. The eleven elements have been simultaneously determined in a standard reference material (SRM) and all results are compatible with a 95% certainty with the certified values. FREMSAAS has been applied to a real sample.Dedicated to Professor Dr. Dieter-Klockow on the occasion of his 60th birthday     

Theoretical calculation of the low laying electronic states of the molecule NaCs with spin-orbit effect

The potential energy curves have been calculated for the 59 lowest electronic states of the molecule NaCs including the spin-orbit effect within the range of 4.5a(0)-20.0a(0) of the internuclear distance R. Using an ab initio method, the calculation is based on a nonempirical pseudopotentials which take into consideration the spin-orbit effect. Gaussian basis sets have been used for both atoms, and the spin-orbit effects have been taken into consideration. The spectroscopic constants have been calculated for 56 electronic states. The components of the spin-orbit splitting have been identified for the states (1,2,4)(3)Pi. The comparison of the present results with those available in the literature shows a very good agreement.     

On the thermodynamic theory of the strength of solids: 5. Energetic characteristics of a crack with a meniscus and ultimate solid strength

The thermodynamic relations describing the formation work of a crack with a meniscus inside it have been analyzed for capillary condensation and evaporation processes. The conformal and depth mechanisms of crack growth have been discussed. It has been shown that the capillary forces alone cannot cause the fracture of a solid upon the formation of a meniscus in a crack. Criteria have been established for the strength upon the brittle fracture, and corrections related to the presence of a meniscus in a crack have been calculated. As a rule, the formation of a meniscus reduces the ultimate strength.     

Orientational dynamics of anthracene in a cyclodextrin functionalized layered solid

Cyclodextrin cavities have been intercalated in a layered metal hydroxide to create hydrophobic nanopockets within the galleries of the layered solid. Anthracene molecules have been included in the anchored cavities by partitioning from a polar solvent. The excitation-emission fluorescence spectra of the included anthracene show a total absence of Stokes shift. The orientational dynamics of the isolated, solvent-free anthracene molecules in the anchored cyclodextrin cavities have been probed by fluorescence anisotropy decay measurements. The results have been compared with those for anthracene included in cyclodextrin cavities in aqueous solutions.     

A microscale Kjeldahl nitrogen determination for environmental waters

A microscale Kjeldahl system has been designed which has been homemade reduced. The digestor unit of a macroKjeldahl system and a modified glassware microdistillation unit have been used. The optimal conditions for digestion and distillation have been established for ammonium and methylamine as model compound of organic amino nitrogen. The optimised procedure has been applied to the determination of Kjeldahl nitrogen in water samples. Recoveries near 100% and good precision have been achieved. This procedure combines nitrogen miniaturized system and the use of a selective ion electrode for ammonia detection. The analysis time was reduced 4.8 times and the analysis cost 6.6 times compared with classical procedure. The residues generated have been also markedly minimized. A preconcentration factor of 4 instead of 1.5 obtained by the macroscale design has been achieved.     

Electrokinetic studies on a thorium oxide membrane : I. Electroosmosis and electrophoresis

Electroosmotic transport of dimethyl formamide through a thorium oxide plug membrahe has been studied and the data have been analysed from the standpoint of thermodynamics of irreversible processes. Electroosmotic flow and eleetroosmotic pressure have been found to be nonlinearly dependent on the applied potential difference. Various phenomenological coefficients have been evaluated from the nonlinear transport equation. Onsager's reciprocity relation has been verified by measurements of streaming potentials. The electrophoretic velocity of thorium oxide particles dispersed in dimethyl formamide has also been found to be nonlinear. Zeta potentials have been evaluated from electroosmotic and electrophoretic data. The results have been explained on the basis of the change in the structure of the electrical double layer. The degree of coupling and the efficiency of electrokinetic energy conversion have been calculated for both electroosmosis and streaming potential.     

Structure and reactions of reduction products in crystalline and polymeric materials by combining pulse radiolysis and ESR

The structure and the reactions of primary oxidation and reduction products in irradiated organic crystals and solid polymers have been investigated. The data from pulse radiolysis with nanosecond time resolution have been combined in a new manner with the data obtained by low-temperature irradiation and ESR spectroscopy. By this combination optical spectra have been assigned, reaction mechanisms have been studied and ESR components have been identified using the kinetic data from pulse radiolysis. The method has been particularly useful in the study of negative-ion radicals in carboxylic acid derivatives, of trapped electrons in polyhydroxy compounds, and of ionic species in polymers.     

Fine structure analysis of the even parity configuration system of Ti I

Even-parity configuration system of Ti I has been considered on the basis of the experimental data available in literature. The fine structure analysis has been performed with the aid of a linked-parameter method of level-fitting calculations in a large multiconfiguration basis. Fine structure parameters have been determined and precise wavefunctions of even energy levels have been evaluated. Appropriate pseudorelativistic Hartree-Fock ab initio calculations of fine structure parameters have been presented for comparison purposes. Configuration interaction effects on even-parity configurations have been discussed.     

A FLASH PHOTOLYSIS STUDY OF INTERMEDIATES IN PHOTOCHEMICAL REACTIONS OF CHLOROPHYLL

Abstract— The photochemical reactions of chlorophyll intermediates in vitro have been studied by the flash photolysis method. The flash excitation of pigment solutions has been shown to involve the population of a chlorophyll triplet state where the oxidation-reduction processes occur. The mechanism and kinetics of pigment triplet decay have been investigated from 20°to — 50°C and the ability of chlorophyll molecules to carry out triplet-triplet energy transfer has been established. The latter phenomenon has been used to show up the role of chlorophyll triplets in the reversible photooxidation reaction with P -quinone. There have been studied initial products of pigment photoreduction with ascorbic acid and phenylhydrazine. Experimental data of the mechanism of the initial oxidation and reduction in chlorophyll photosensitized reactions have been analysed. There have been also obtained the differential spectra of chlorophyll triplets and radicals. A calculation has been made of rate constants for a few elementary reactions.     

Copper ferrocyanide — polyurethane foam as a composite ion exchanger for removal of radioactive cesium

A method has been developed for the removal of cesium from the aqueous radioactive waste using a composite ion-exchanger consisting of Copper-Ferrocyanide Powder (CFC) and Polyurethane (PU) Foam. Polyvinyl acetate has been used as a binder in the preparation of CFC-PU foam. The physical properties of CFC such as density, surface area, IR stretching frequency and lattice parameters have been evaluated and also its potassium and copper(II) content have been estimated. Optimization of loading of CFC on PU foam has been studied. The CFC-PU was viewed under microscope to find out the homogeneity of distribution. Exchange capacities of the CFC-PU foam in different media have been determined and column studies have been carried out. Studies have been undertaken on extraction of cesium from CFC foam and also on digestion of spent CFC-PU foam and immobilization of digested solution in cement matrix. The cement matrices have been characterized with respect to density, bio-resistance and leaching resistance.     

Studies on the radiolytically produced transients of neutral red: triplet and reduced radicals

The spectral and kinetic properties of reduced radicals and the triplet state of neutral red (NR), a phenazine-based dye, have been investigated using pulse radiolysis technique. A mixed water-isopropanol-acetone solvent has been used to study the reduced radicals of NR for a wide pH range of about 1-13, due to limitation of solubility of the dye in aqueous solutions particularly above pH 8. From pH-dependent absorption studies it has been established that the reduced radicals of NR can exist in four different prototropic forms in solution. Three pKa values for the corresponding prototropic equilibria have been estimated. The formation and decay rate constants of reduced radicals have also been measured. The triplet state characteristics of the dye have been investigated in neat benzene solutions, both in the presence and in the absence of triplet sensitizers. The T1-->Tn absorption spectrum and decay kinetics of the triplet state have been measured. The triplet state energy (ET) of NR in benzene have been estimated to be within 36-42 kcal mol-1, using an energy transfer method.     

Coupled calculations of vibrational frequencies and intensities. III. IR and Raman spectra of ethylene oxide and ethylene sulfide

The experimental IR and Raman spectra of ethylene oxide have been reinvestigated with particular attention to the intensities. The absolute IR intensities have been measured for the gaseous state. The spectra have been simulated by using a normal coordinate analysis coupled with a CNDO determination of the intensities. The intensity calculation using polarization functions appears to be more reliable than the standard version. Furthermore, the force field has been extended for ethylene sulfide.     

Phase structure of silanol-modified ethylene-vinyl acetate copolymers

For (ethylene-vinyl acetate copolymer)-tetraethoxysilane and (ethylene-vinyl acetate copolymer)-polydimethylsiloxane systems, the solubility of components has been studied in a wide range of temperatures and compositions. Phase diagrams have been constructed, pair interaction parameters have been calculated, and diffusion coefficients and activation energies of diffusion have been estimated. The temperature and concentration ranges of a change in solubility related to chemical interactions between the components have been revealed, and the structure of the modified copolymers has been studied. On the basis of the kinetic data on the movement of isoconcentration planes in diffusion zones of component mixing, time intervals corresponding to the onset of the chemical reaction between the components have been determined and the apparent activation energies of the process have been computed. Complex-shaped binodal and boundary curves have been interpreted within the framework of the classical Flory-Huggins theory.     

Continuous chromatographic separation process: simulated moving bed allowing simultaneous withdrawal of three fractions

Continuous counter-current chromatographic separation has been carried out in a simulated moving bed system (SMB). We have worked with a SMB pilot plant (8 columns, 4.4 litres of resin each) which allows the continuous withdrawal of two different fractions. A mixture of glucose-fructose has been separated. To calculate the concentration profile within the separator an axial dispersed plug flow model and an equilibrium stage model have been employed; software has been created to simulate the behaviour of the separator. The necessary parameters of the mode: the adsorption equilibrium constant, the height equivalent to a theoretical plate and the bed voidage, have been acquired experimentally from elution chromatography measurements. The results calculated by simulation give a good representation of the experimental concentration profiles; other separations like xylitol-arabitol have been simulated. The influence of some factors like desorbent flow-rate, feed flow-rate and the bed voidage have been studied using the software. Once the system has worked in a two withdrawal way, an extension of the pilot plant has been constructed so as to obtain a third one. The necessary parameters of the three withdrawal model will be studied.     

Standard molar enthalpies and volumes of adamantane in methanol,ethanol, acetone,andn-dodecane. Interpretation using the scaled-particle theory

The volumes and enthalpies of solution of adamantane and of cyclohexane in methanol, ethanol, acetone, and n-dodecane have been measured as a function of concentration at 25°C. The standard molar volumes and enthalpies of adamantane have been resolved into cavity and interaction terms. The former have been calculated from the equations of the scaled-particle theory whereas the latter have been deduced from a model which assumes some proportionality between adamantane-solvent and cyclohexane-solvent interactions. The model, which had been previously verified with normal liquids, now also proves to be very satisfactory with solvents involving strong, nonadditive interactions.     

Physicochemical studies of octadecyl-trimethyl-ammonium bromide: a critical assessment of its solution behavior with reference to formation of micelle, and microemulsion with n-butanol and n-heptane

Octadecyl-trimethyl-ammonium bromide (C18TAB) is a much less studied representative in the alkyltrimethylammonium halide surfactant series. A comprehensive study of its normal and reverse micelle (microemulsion) formation has been herein conducted by the methods of conductometry, tensiometry, fluorimetry, and microcalorimetry. The energetics of its air/liquid interfacial adsorption and self-association in aqueous solution have been examined. The phase behavior of its combinations with water, n-butanol, and n-heptane in the formation of microemulsions have been investigated with identification of a variety of phases. The energetics of formation of water dispersion in oil (w/o) has been evaluated from dilution experiments conducted at different temperatures. From the results, structural parameters of the droplets have been determined at different [water]/[surfactant] mole ratios (omega) and temperatures. The w/o dispersions have evidenced both volume- and temperature-induced conductance percolation. The results have been treated in light of the Scaling equations, and the associated parameters for the process have been determined. The activation energies for the temperature-induced percolation process of the w/o dispersion have been evaluated and assessed.     

Infrared near-field detection of a narrow resonance due to molecular vibrations in a nanoparticle

Di-iron nonacarbonyl particles on a gold surface have been imaged using an apertureless near-field scanning infrared microscopy. First and second harmonic detection, with and without an auto-homodyning option, have been used to collect the near-field spectrum of a single vibrational mode of the bridging carbonyls in di-iron nonacarbonyl nanocrystalline flakes on a gold surface. The experimental results have been compared to two theoretical models, a static image-dipole effective medium and an image dipole modified by a Fresnel coefficient for the appropriate observation angle. The calculations have taken into account the roughness of the gold film. The phase dependence of the near-field contrast has been investigated using broadband and tunable CO2 lasers. Particle size effects on contrast and spatial resolution have been studied to determine the limits of applicability of the half-space approximation.